-LRB- CNN -RRB- -- Schools , major roads and an airport remained closed Tuesday , as a thick cloud of filthy smog smothered the northeastern city of Harbin .

Meteorologists in the city , which is famous for its annual ice festival , issued a red alert for fog at 5 a.m. Tuesday , with visibility in some central areas of the city down to less than 20 meters -LRB- 65 feet -RRB- , the state-run Xinhua news agency reported .

Video from China 's state-run CCTV showed some people -- obscured by smog even just steps away -- wearing masks over their mouths as they walked in the province . Some drivers who braved the roads flashed hazard lights .

Kindergartens , primary and junior middle schools were ordered to suspend classes for a second day , while Harbin Taiping International Airport remained closed -- with 250 flights canceled on Monday alone , according to Chinese state media .

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Hazardous levels

Pollution levels remained far above international standards , as the city 's monitoring stations on Tuesday showed that concentrations of PM2 .5 -- the tiny airborne particles considered most harmful to health -- were more than 30 times the World Health Organization 's recommended standard , the state-run China Daily reported .

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Government officials blamed the smog on a lack of wind and farmers burning crop stalk after their autumn harvest , though the city 's coal-burning heating system , which was recently started , is also a likely factor . Harbin 's environmental bureau has also conducted checks on factories known to discharge pollutants , the China Daily report added .

Extreme conditions

Fang Lijuan , the city 's chief meteorologist , said it was very rare for the city to suffer such extreme conditions .

`` There has been no strong wind and the level of humidity is high , '' she said , in quotes carried by China Daily .

Residents of this city of 10 million people were also surprised by the thick smog .

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`` The pollution is indeed very bad , we can only see things within 100 meters , and yesterday it was 20-30 meters . We can smell the smoke in the air , '' one man , who identified himself as Mr. Ren , told CNN .

`` The smog started about four days ago ... I heard all face masks in Harbin are sold out . People are very angry about this and there is a lot of discussion over the Internet .

`` The main reason is Harbin started its heating and the main resource is coal . Every year at this time , the air quality is bad -- but this year is especially polluted . ''

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Naming and shaming

Last month China announced plans to start listing its top ten most air-polluted cities every month in the hopes that national humiliation will push positive environmental action .

`` We must put air quality control as an ecological red line for economic management and social development , '' China 's Vice Premier Zhang Gao Li said in a statement as he announced the new policy at the 18th Air Pollution Control Conference in Beijing .

Chinese officials did not say when the first list would be announced , but the northern megacities of Beijing and Tianjin , as well as the surrounding provinces of Hebei , Shanxi , Inner Mongolia and Shandong have signed onto an official plan to speed up air pollution control measures .

China 's capital often suffers with hazardous pollution levels and smog . An explosion in the number of cars on the roads , as well as industrial pollution are seen as the main contributors .

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CNN 's Feng Ke in Beijing contributed to this report .

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Visibility in some central areas of the city down to less than 20 meters -LRB- 65 feet -RRB- , Xinhua said

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Pollution levels 30 times the World Health Organization 's recommended standard

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Government officials blame lack of wind as well as farmers burning crop stalks